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Regulation of Seedling Height in Container-Grown Spruce
Using Photoperiod Control 1
A. M. Eastham2
Abstract. --In 1989, container-grown white x
Sitka spruce (Sxs) seedlings were subjected to a
15h day, either static or dynamic method of
blackout treatment, for four weeks to promote
budset and regulate height.
The blackout treated
seedlings were shorter, and had less shoot mass
compared to controls without any effect on stem
diameter.
Control
seedlings acquired coldhardiness slower than blackout treated seedlings,
and the dynamic method acquired cold-hardiness
slower than the static method.
Under controlled
conditions, days to budbreak in spring was three
days
earlier
for
blackout treated
seedlings
compared to controls. In 1988, a larger experiment
with six seedlots and 12 blackout treatments,
applied using dynamic method, was conducted which
included the same seedlot as in 1989 and results
are compared. All seedlings were lifted and frozen
stored.
In May 1989, all treatments for all
seedlots were outplanted in nursery beds and four
seedlots were also planted in their respective
regions. First year field assessments indicated a
reduction in height growth with 13 h daylength for
Engelmann spruce, but not for white x Sitka spruce
seedlings.
Blackout treatments had little or no
effect on phenology.
INTRODUCTION
In British Columbia we produce
container-grown seedlings of white
(Picea glauca (Moench), Englemann (g.
engelmannii Parry), and Sitka spruce (g.
sitchensis (Bong.) Carr.) and commonly
we are dealing with naturally occurring
hybrids of these three species.
Regulating height growth at the end of
the season is a common problem for
nurserymen, particularly in nurseries
located in northern latitudes with
naturally long days during the growing
season.
1
Paper presented at Western Forest
Council
1990
Conference,
Roseburg,
Oregon, August 13-17, 1990.
2
Research
Scientist,
British
Columbia Ministry of Forests, Red Rock
Research Station, R.R. #7, RMD 6, Prince
George, B.C. V2N 2J5, canada
Nurserymen use both drought and
nutrient stress to regulate seedling
height {Macey & Arnott 1986). Both of
these stresses appear to regulate height
by slowing growth rather than promoting
early budset. Shortened daylengths
imposed by blackout systems promote
early budset to regulate seedling height
(Dormling et al. 1968). The advantages
of using blackout over drought and
nutrient stressing are:
1) seedlings are not stressed,
2) crop response is uniform, and
3) it is easier to impose.
Research on the use of blackout
culture to promote budset and regulate
height in spruce seedling production
began in 1987 at the B.C. Ministry of
Forests, Red Rock Research Station
(RRRS), Prince George, B.C. Results
from the 1987 growth chamber study
(Hawkins and Hooge 1988) ·and preliminary
results from 1988 (Hawkins and Draper
1988) were presented at the Combined
Meeting of the Western Forest Nursery
247
Associations held August 8-11, 1988 in
Vernon, B.C. This paper presents some
of the results from experiments
conducted during 1988 and 1989,
including first year field performance
of blackout cultured seedlings.
2-4
22
20
18
OBJECTIVE
Experiments were conducted at RRRS,
a northern latitude research facility
(lat. 53° 45'N; long. 122° 41'W), to
determine the effect of short day
treatments on height growth of spruce
seedlings in order to provide nurserymen
with operational guidelines for length
of day (hours) and duration (weeks) of
blackout treatment. The effects of
blackout culture on cold-hardiness,
dormancy, and field performance were
also investigated.
MATERIALS AND METHODS
Spruce seeds (Sxs) of SL3958 (Lat.
55° OO'N, Long. 128° 45'W; Elevation 400
m) from the Prince Rupert Region were
stratified at 2°C for three weeks prior
to sowing March 16, 1989 in BC/CFS 313
styroblocks using a 2:1 peat:vermiculite
(vjv) growing mix. The styroblocks were
placed in a research polyhouse at the
Red Rock Research Station, Prince
George, B.C. and grown using the culture
described by Hawkins and Draper, 1988.
Seedlings were grown under a 23h
photoperiod until blackout treatments
began on June 28, 1989.
The blackout treatments were
ambient (control), and a 15h daylength
for four weeks applied using either the
static or the dynamic method of imposing
short days (fig. 1). The static method
is simply a constant night length for a
given period of time and is the standard
method used in crop production. The
dynamic method parallels the natural
declining day length over the treatment
period so that the daylength gradually
shortens during the weeks of treatment,
offset from the ambient daylength by a
predetermined, constant number of hours.
Following treatment, seedlings were
grown in the polyhouse under ambient
conditions until lift. The lift date
(Nov. 24, 1989) for all seedlings was
based on the results of freezer tests
conducted every one to two weeks
starting Sept. 15, 1989.
248
18
6
1-4
~
12
;
10
o4
DAYS SINCE SOWING (16 MARCH 1989)
Figure 1.--The natural daylength
(includes civil twilight) at RRRS
(C), showing the daylengths imposed
by the static (A) and dynamic (+)
blackout treatments for four weeks
from June 28 to July 27, 1989.
Ten seedlings per treatment were
selected at random and exposed to three
or four preset temperatures during each
test with a constant soc h- 1 ramp and 5
min soak at each plateau temperature.
The temperatures used on each date were
decreased gradually as seedlings
acquired cold hardiness. Following
freezing, 5 seedlings from each
treatment were potted into 1-gal nursery
pots for a total of two pots per
treatment. Seedlings were placed in
controlled environment growth chambers
and assessed one week later for percent
foliage browning. At lift, 150
seedlings per treatment were
systematically selected and measured for
height, stem diameter, shoot dry weight,
and root dry weight. As well, 15 blocks
for each treatment were assessed for
percent of seedlings reflushing.
Following lift, seedlings were stored at
-2°C until spring 1990.
Twenty seedlings per treatment were
selected at random from storage in May
1990, potted with five seedlings per pot
and placed in controlled environment
chambers for determination of days to
budbreak (DBB) and root growth capacity
(RGC). Two pots were placed in a
chamber with dayjnight temperatures of
25°C/20oc, and two in a chamber with
15oC/5oC.
In 1988, spruce seedlings from six
seedlots were exposed to four blackout
daylengths, each applied for three
durations as described by Hawkins and
Draper, 1990. All seedlings were lifted
and frozen stored.
On May 13, 1989, 99 seedlings per
treatment were outplanted at RRRS and
terminal bud phenology assessed using
the codes in Table 1. End of season
height and stem diameter increment were
determined on 54 seedlings per
treatment.
Table 1.--Phenology coding and description of each code used during the
first field season following
outplanting of blackout treated
spruce seedlings.
Code
0
1
2
3
4
5
Description
resting spring terminal bud
bud swell
bud flush/shoot elongation
lateral buds forming
terminal buds forming
resting fall terminal bud
As well, four seedlots were
outplanted in their respective regions
through the cooperation of the Regional
Forest Science staff. This paper
reports the terminal bud phenology, and
seedling height and stem diameter
increment after the first year in the
field for Engelmann spruce seedlot 4311
(Lat 50° 55', Long. 120° 05'; Elevation
1435 m) from the Kamloops Region.
Twenty-five seedlings per each of the
seven original blackout treatments were
planted May 30, 1990, at McGillivray
Lake in the ESSFdc2 1 ; elevation 1480 m;
aspect SE; logged 1987 and blade
scarified.
dry weight compared to untreated
seedlings (table 2). Stem diameter and
root dry weight appeared unaffected by
treatment, but the shoot:root ratio was
lower for treated seedlings due to the
decrease in shoot dry weight. The
control seedlings, if graded using the
B.C. stock specifications 1 , would have
been overheight (maximum = 300 rom) and
culled for low root dry weight (cull =
0. 5g) .
Seedlings subjected to the static
blackout treatment (constant 15h day)
were significantly shorter with greater
stem diameter, compared to those
subjected to the dynamic blackout
treatment (table 2). With both methods
of applying blackout, reflushing
occurred in 26-30% of the seedlings for
static and dynamic respectively. The
static treatment tended to have greater
root dry weight and shoot dry weight but
not significantly different from the
dynamic treatment.
Cold-hardiness was acquired earlier
in the growing season by blackout
treated seedlings (fig. 2), and the
static method appeared to accelerate the
acquisition compared to the dynamic
method. By Nov. 17, 1989 (just prior to
lifting) 55% of th~ foliage on control
seedlings was killed by a test
temperature of -18°C compared to only
35% for the dynamic treatment, and 4%
for the static treatment. Eleven days
later (Nov. 28) the percent injury was
down to only 18% for both control
seedlings and those subjected to the
dynamic blackout, and the seedlings from
the static treatment remained at 3-4%.
After six months of frozen storage,
the DBB for control seedlings was three
days longer than for blackout treated
seedlings (table 3) under warm
temperature conditions (25°C/20°C D/N).
With the cooler temperature regime of
15°C day and soc night, the treatment
differences in DBB disappeared (table
3), and with either regime there was no
difference between static and dynamic.
RESULTS
First year field performance
Static vs Dynamic 1989
The 15h for four week blackout
treatments resulted in spruce seedlings
that were shorter and had lower shoot
1
B . C . M1n1stry
' '
of Forests
Biogeoclimatic Zones Classification
System.
First year field height growth and
stem diameter increment appeared to be
unaffected by the blackout treatments
they received during the nursery culture
1B
' ' t ry of Forests,
.c. M1n1s
Silviculture Branch 1989 Stock
Specifications for Sitka spruce crosses
stock type PSB313A/B.
249
Table 2.--End of season seedling height, stem diameter, shoot dry
weight (SDW), root dry weight (RDW) and root:shoot ratio
following a 15 hour day blackout treatment for four weeks
starting June 28, 1989 for SL3958.
Height
(mm)
Blackout
Treatment
SDW
(mg)
Stem dia.
(mm)
RDW
(mg)
Ratio
S:R
Control
386 ± 5. 5 1 3.2 ± 0.05
2489 ± 85
494 ± 22
5.0
Dynamic
283 ± 6.3
3.2 ± 0.06
2011 ± 77
508 ± 23
4.0
Static
265 ± 6.0
3.4 ± 0.06
2030 ± 80
546 ± 23
3.7
1
Mean ± SE, n
150.
Table 3.--Days to budbreak of spruce
seedlings (SL 3958) in spring 1990
following frozen storage for
control, dynamic, and static
blackout treatments with the tests
conducted at two temperatures
(day/night)
MEAN FOLIAGE BROWNING (%)
120
BLACKOUT TREATMENT
1oo
•
Control
·
rs=J Dynamic
80
60
40
20
0
Sep27
Oct 19
Nov 1
DATE
Nov17
Blackout
Treatment
Days to budbreak
25°C/20oC 15oc;soc
Control
10 ± 1. 0 1
11 ± 0.5
Dynamic
7 ± 0.4
11 ± 0.4
Static
7 ± 0.5
10 ± 0.5
Nov28
1
Mean ± SE, rep
Figure 2.--Development of cold hardiness
expressed as percent mean foliage
browning assessed one week after
frost hardiness tests for control
and blackout treated spruce
seedlings, SL3958. Test
temperature on Sept. 27 and Oct. 19
was -13oc, on Nov. 1 was -17oc, and
on Nov. 17 and Nov. 28 was -18°C.
for Engelmann spruce seedlings SL4311
(table 4). The trend for Sitka x white
spruce seedlings showed an increase in
first year height growth with both 13h
and 15h photoperiods compared to 17h and
controls. Averaging over treatment
duration (weeks), the 13h photoperiod
increased 149 mm in height and the 15h
increased 146 mm compared to 116 mm and
91 mm for 17h and control, respectively
(table 4). Stem diameter increment
remained unaffected by blackout
treatment.
250
5 seedlings, n=2
The opposite effect was observed
for SL4311 when planted in a
regeneration site (table 5). The height
growth for the 13h photoperiod was 111
mm (2 wk + 6 wk) compared to 130, 140,
and 128 mm for 15h, 17h, and control
treatments, respectively. Again, there
appeared to be no effect on stem
diameter growth due to blackout
treatment during the nursery culture
year.
Terminal bud phenology during the
first year in the field was not affected
by nursery blackout treatments for
Engelmann spruce seedlings (table 6).
On June 12, 1990 100% of all treated
seedlings had flushed and 80% of the
controls. However, within the next six
days all the controls had flushed as
well. By Aug. 22, 1990, all seedlings
in all treatments had set bud with the
Table 4.--Seedling height increment and stem diameter increment
following first year in the nursery bed at Red Rock Research
Station for two seedlots 4311 and 3958, Engelmann spruce
and sitka x white hybrid spruce, respectively. 1
Height increment (nun)
Treatment
day (h) weeks
SL 4311
SL 3958
Diameter increment (nun)
SL 4311
SL 3958
13
2
4
6
123 ± 62
140 ± 21
126 ± 10
138 ± 15
166 ± 18
144 ± 14
3.6 ± 0.6
4.4 ± 0.4
4.2 ± 0.3
2.5 ± 0.5
3.5 ± 0.3
3.9 ± 0.2
15
2
4
6
148 ± 4
132 ± 11
163 ± 10
129 ±
157 ±
153 ±
5
9
8
3.5 ± 0.2
3.8 ± 0.4
3.9 ± 0.1
3.2 ± 0.4
3.1 ± 0.3
4.0 ± 0.4
17
2
4
6
135 ± 5
126 ± 4
152 ± 12
97 ±
115 ±
135 ±
4
1
6
3.3 ± 0.2
3.1 ± 0.4
4.0 ± 0.3
3.4 ± 0.1
3.6 ± 0.4
3.1 ± 0.2
19
2
4
6
138 ±
151 ±
135 ±
81 ± 13
95 ± 2
98 ± 4
3.7 ± 0.3
3.8 ± 0.2
3.2 ± 0.6
2.7 ± 0.2
3.3 ± 0.1
2.6 ± 0.5
4
3
5
1Hawkins and Draper, 1990
2Mean ± SE, rep = 18 seedlings, n = 3.
Table 5.--Mean seedling height increment
and stem diameter increment
following first year outplanting in
Kamloops Region for Engelmann
spruce SL4311
Treatment
Height inc.
day (h) weeks
(nun)
(nun)
13
2
6
115 ± 71
107 ± 2
1.4 ± 0.06
1.7 ± 0.05
15
2
6
135 ± 6
125 ± 5
1.4 ± 0.04
1.7 ± 0.07
17
2
6
140 ± 5
140 ± 5
1.4 ± 0.08
1.5 ± 0.04
128 ± 5
1.4 ± 0.08
Control
1
Diameter inc.
Mean ± SE, rep
5 tree row, n=5.
exception of the 13h 2 wk treatment
which had 5% of the seedlings without a
resting terminal bud. Within one week
100% of the 13h 2 wk treatment seedlings
had a final terminal bud, and no
reflushing occurred during the rest of
the growing season.
In the nursery bed at RRRS, the
same seedlot showed the same phenology
at budflush, i.e., no treatment effect
(table 7). Terminal bud scale formation
began nine weeks after planting (midJuly), and resting terminal buds
developed in mid-August, 14 weeks after
planting. However, in mid-August,
reflushing was observed on seedlings
from both the 13h, and 15h, for 2 wk and
6 wk treatments (table 7). This
resulted in as much as a 14 day delay in
final budset in the 13h photoperiod for
the longest duration (6 wks).
The Sitka x white hybrid seedlings
SL3958 continued to elongate longer into
the growing season and did not start the
final budset stage (stage 5) until midSept. for control seedlings, and even
later in Sept. and Oct. for treated
seedlings (table 8). Seedlings from the
13h photoperiod appeared to set bud even
later than either the 15h or 17h
photoperiods.
DISCUSSION
A complete report of the 1988
experiment which included SL3958 and
251
Table 6.--Spruce seedling terminal bud modal phenology class
during the first year in the field in Kamloops Region.
Seedlings wer.e produced in 1988 at RRRS using four
daylengths and two durations of blackout culture.
Phenology Code 1
Blackout
Treatment
day weeks
13h
2 wk
6 wk
0
0
2
2
2
2
2
2
3
3
3
3
4
4
5
5
5
5
15h
2 wk
6 wk
0
0
2
2
2
2
2
2
3
3
3
3
4
4
5
5
5
5
17h
2 wk
6 wk
0
0
2
2
2
2
2
2
3
3
3
3
4
4
5
5
5
5
0
2
2
2
3
3
4
5
5
Control
Julian Day
Month
163 170 182 194 205 220 234 248
I
I
June
July
I Sept.
I
I Aug.
1989 field growing season
150
May
1
Codes as described in Table 1.
Table 7.--Spruce seedling terminal bud modal phenology class
during the first year in the nursery bed at RRRS for SL4311.
Seedlings were produced in 1988 using four daylengths and
three durations of blackout culture 1 •
Blackout
Treatment
day weeks
Phenology Code 2
2 wk
13 h 4 wk
6 wk
0
0
0
1
1
1
1
2
2
2
2
2
2
2
2
3
3
3
4
3
3
4
4
4
(4)
4
(4)
4
5
(5)
4
5
4
5
5
5
2 wk
15 h 4 wk
6 wk
0
0
0
1
1
1
1
1
1
2
2
2
2
3
3
3
3
4
3
3
4
4
4
(4)
4
(4)
4
4
5
5
5
5
5
5
5
2 wk
17 h 4 wk
6 wk
0
0
0
1
1
1
1
1
1
2
2
2
2
2
2
3
3
3
3
3
3
4
4
4
4
4
4
5
4
5
5
5
5
5
5
5
2 wk
19 h 4 wk
6 wk
0
0
0
1
1
1
1
1
1
2
2
2
2
2
2
3
3
3
3
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
Julian Day
Month
2
133 139 149 157 171 180 194 209 223 235 249 275
I
I
May
July IAugust I September
June
I
I
1989 field growing season
1
Adapted from Hawkins and Draper,
2
Codes as described in table 1.
3
1990.
Brackets indicate >20% terminal bud flushing.
252
Table a.--spruce seedling terminal bud modal phenology class
during the first year in the nursery bed at RRRS for SL3958.
Seedlings were produced in 1988 using four daylengths and
three durations of blackout culture 1 •
Blackout
Treatment
day weeks
:.,
'
Phenology Code 2
2 wk
13 h 4 wk
6 wk
0
0
0
1
1
1
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
4
4
4
5
4
4
2 wk
15 h 4 wk
6 wk
0
0
0
1
1
1
1
2
1
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
4
4
3
4
4
4
5
5
4
2 wk
17 h 4 wk
6 wk
0
0
0
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
3
3
3
4
3
3
4
3
3
4
4
3
4
4
4
5
5
4
2 wk
19 h 4 wk
6 wk
0
0
0
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
3
3
3
4
3
3
4
3
4
4
3
4
5
4
4
5
5
5
Julian Day
Month
133 139 149 157 171 180 194 209 223 235 249 275
I
I
May
June
July IAugust I September
I
I
1989 field growing season
1
Adapted from Hawkins and Draper, 1990.
Codes as described in Table 1.
2
SL4311 can be found in Hawkins and
Draper (1990). The response of the
vigorous Sitka x white hybrid spruce
seedlings (SL3958) to a four week, 15h
day blackout treatment varied in 1989
from the response in 1988 in both root
dry weight and percent reflushing. The
difference in mean root dry weight
between controls and treated was 180 mg
in 1988, but only 14 mg in 1989.
Hawkins and Draper (1990) reported only
2% reflushing in this seedlot and these
were lateral buds on seedlings in the
13h daylength treatment. This is
minimal reflushing compared with the 26
- 30% recorded in 1989 which included
terminal bud reflushing as well. The
two growing seasons did differ as
control seedlings in 1989 were 77mm
taller than those in 1988, and had 12%
less root dry weight.
Hawkins and Draper (1990) have
given many reasons for using the dynamic
method for applying blackout and one
possible positive feature is that this
method may give adequate height
regulation without negatively impacting
on seedling physiology. Cold hardiness
development was accelerated by blackout
treatments in both years, however in
1989, the dynamic method produced
seedlings that behaved more like the
control seedlings (figure 2).
Days to budbreak for SL3958 were 10
days in 1989 compared to seven days in
1990. Hawkins and Draper (1990) reported
that DBB decreased with decreasing
daylength and increasing duration.
However, there was only five days
difference between controls (12 days)
and the severist blackout treatment (13h
for 6 weeks=? days). They observed'the
same trend in white and Engelmann spruce
though the difference was only two days
for the same comparison.
In the nursery bed there was little
or no treatment effect on budflush or
budset except with the 13h daylength.
For SL4311 on the regeneration site, all
treatments were at 100% budset by August
22, 1990 except the 13h for two week
blackout treatment which was at 95%.
This is in contrast to the results for
black spruce in Ontario where short day
seedlings remained actively growing for
three to six weeks longer than untreated
(Odlum and Columbo, 1988). The
253
difference in response between nursery
bed and field in our study was the
reflushing that was recorded in the
nursery bed. This may be related to the
fertilization and irrigation practised
in the nursery compared with the drier
regional site.
First year after planting terminal
height growth was unaffected by the
previous blackout treatments for SL4311
in nursery beds. Results from the
outplanting in the region showed a
reduction in height increment for
seedlings receiving the 13h daylength
compared to all other treatments. This
same trend was observed in the three
other regional outplantings (data not
presented). The difference in height
increment between nursery and field
again may be due to the watering,
fertilizing, and weeding that occurred
in the nursery.
Acknowledgements
My thanks to R. Eng, B. Hooge, and
T. Letchford for technical assistance;
A. Vyse, Regional Forest Science Officer
for cooperation with outplanting
project; and K. Dale for preparation of
this paper.
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abies (L.) Karst. Some basic
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254
Hawkins, C.D.B., and D.A. Draper. 1988.
Height control of interior spruce
by means of photoperiodic
induction.
Proc., Combined meeting
of the Western Forest Nursery
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B.C. (ed. T.D. Landis). pp 45-49.
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Nursery and first field season
effects following blackout
treatment of six seedlots of spruce
at Red Rock Research Station. (FRDA
report in prep.)
Hawkins, C.D.B. and B.D. Hooge. 1988.
Blackout and post planting bud
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-In Proceedings, Combined meeting
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effect of moderate moisture and
nutrient stress on bud tormation
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spruce seedlings. Can J. For. Res.
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Odlum, K.D. and S.J. Columbo. 1988.
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following year.-In Proceedings,
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